Visual attention pathway mapped

Given the copious amount of sensory stimuli in our surroundings, it is not an easy feat to focus on any one particular piece of information. Take our visual system, for example: how is it possible to locate your friend in a busy lecture hall?
Neuroscientists at the Carnegie Mellon University, in collaboration with researchers at the University of Pittsburgh, identified the connections between different brain regions used to pay attention to selective visual stimuli.
It has long been known that the occipital lobe, or visual cortex, located at the posterior part of the cerebral cortex, is responsible for the processes of visual information. Photons of different wavelengths strike the photoreceptors in the eyes, subsequently activating a series of neurons, eventually reaching the visual cortex.
Specialized neurons in this area are responsible for encoding different types of stimuli. For example, there are neurons that respond specifically to a particular direction of motion in visual area V5, also known as the MT cortex.
The parietal lobe, on the other hand, has been known to receive input from various areas in the brain, including the visual cortex. The information is then processed, thus allowing the subject to selectively pay attention to limited sensory stimuli, singled out from the copious amount available.
However, although it has been known that the visual cortex communicates to the parietal lobe, the specific connections have always been a mystery. Do neurons of the visual cortex each correspond to a particular neuron in the parietal lobe, or is the association amongst a broader population of neurons?
This study demonstrates that the one-to-one mapping between neurons is not limited to the photoreceptors in the retina. Instead, attention also seems to be a process resulting from one-to-one connections between neurons in the visual cortex and those in the parietal lobe.
There are two parts to this study. In the first part, several functional brain scans were used to identify regions responsible for processing of visual stimuli and attention. Participants were asked to fixate on a dot at the center of the screen, while six stimuli flashed around the dot.
In the second task, participants were then asked to respond to each stimuli one at a time, while their brains were scanned to determine activity levels in the occipital and parietal cortices.
The second part of the experiment was geared toward determining the anatomical information of the white matter connectivity. Participants were scanned without engaging in any tasks. The results were then combined with those of the first part of the study to determine the connectivity of white matter tracks (axons) during functional tasks of part one.
Results suggest that the connections are mapped systematically, which means that there are direct connections between visual field locations in the occipital cortex and corresponding regions of the parietal lobe.
Furthermore, the scans were performed using "diffusion spectrum imaging," which is a new technique developed at the Carnegie Mellon University and University of Pittsburgh.
Combined with high-resolution tractography, results of this study show a higher level of accuracy in terms of connections mapped, when compared to those determined using other traditional methods.
Knowing that training can alter white matter connectivity, researchers hope to improve attention by filtering out irrelevant information through training. It is hopeful that this will provide further insight to visual and attention deficit disorders.